For a conventional dual polarization radiation unit, it is typical that two polarized radiation oscillators have the consistent structural size and shape. Moreover, each radiation oscillator is disposed in a same plane. In other words, the two polarized radiation oscillators will overlap each other if rotated 90 degree relative to each other. Though this design to certain extent improves radiation performance consistency of two polarizations, considering avoidance of interference caused by power feeding, rather than disposed in a same plane, feeding ports of two polarizations have to be disposed in different planes. Due to difference in height of the feeding ports and difference in other correspondingly produced boundary conditions, radiation performance value of the two polarizations of an array antenna consisted of above mentioned several consistent radiation units will show certain difference.
With the continued widening of working frequency of mobile antenna, in particular when operated at ultra wide frequency (for example at 1710˜2690 MHz), inconsistency of two polarizations becomes significant for either single radiation unit or array antenna. For instance, at a same frequency, important parameters of two polarizations such as H-Plane Half Power beam-width, front to rear ratio, cross polarization discrimination, polarization consistency, and H-plane beam deflection exhibit obvious inconsistency. In addition, this kind of inconsistency will be increased with increase of electrical down-tilt angle of electrically adjustable antenna and is difficult to be eliminated.
At present, to improve network quality and uniform covering of uplink and downlink of network by network operators, high requirements have been proposed for consistency of radiation performance of two polarizations of base station antenna. Radiation units and array antenna consisted of them will almost not meet these requirements of network operators.
If the radiation oscillators of two polarizations are located in a plane at the same height, coupling between two polarizations in a single radiation unit will be increased, and coupling between two polarizations of the array antenna will be increased as well, thus resulting in difficulty in improvement of isolation of wide frequency band array antenna.
Given above situations, person of the art faces challenges on how to maintain uniformity of both radiation performance and isolation of two polarizations.